1. Field of the Invention
The present invention relates to a digital camera including a lens barrel capable of retracting at least one of a plurality of lens groups out of an optical axis when the lens barrel is in a collapsed position, and a mobile information terminal apparatus using the digital camera.
2. Description of Related Art
A high performance imaging device, such as a digital camera, is often provided with a lens barrel having a zoom lens function capable of changing a focal distance. Such imaging devices can be made more compact when they have a collapsible lens barrel in which a plurality of lens groups can be collapsed when not in use for making a photograph. Furthermore, because of the demand for such compact imagine devices having a greatly reduced thickness, it is important to reduce the thickness of the lens barrel in collapsed condition to the maximum extent possible.
As a technology to cope with the demand for reduction in thickness of the lens barrel, there has been used a collapsible lens barrel in which a lens frame retaining therein a plurality of lens groups is collapsed into the imaging device when not in use, and one of the lens groups is retracted out of an optical axis of the lens groups when the lens groups are collapsed. A technology for retracting one of lens groups out of an optical axis is disclosed in, for example, JP No. 2003-315861 A (Patent Document 1) and JP No. 2003-149723 A (Patent Document 2). According to the structures disclosed in these Patent Documents 1 and 2, since one of a plurality of lens groups disposed on the optical axis is retracted out of the optical axis when the lens groups are collapsed, the entire dimension of the lens barrel in a direction of the optical axis can be reduced.
However, in the structures disclosed in Patent Documents 1 and 2 as described above, the lens retracted out of the optical axis is substantially positioned within a collapsible lens frame provided in the lens barrel to retain therein the lens groups, even after the lens is retracted. Therefore, a space sufficient to contain the retracted lens must be provided in the lens frame. Providing such space in the lens frame results in a larger diameter of the lens frame, eventually a larger size of the lens barrel within a plane transverse to the optical axis. Accordingly, there is a problem that the conventional lens barrel has a large diameter by provision of the space containing the retracted lens in the lens barrel.
Therefore the inventors of this application disclosed formally in JP No. 2006-330657A (Patent Document 3, Referring to Specification and FIGS.) a lens barrel that reduces thickness of the imaging device without enlarging the size of it. The lens barrel disclosed in the Patent Document 3 includes a first lens group, a second lens group, a third lens group and a fourth lens group disposed in a sequence from a subject side to an image side wherein each is retained in a frame respectively. In particular, the third lens group is configured as that it is restrained in a retractable frame rotatable around a main-guide shaft member parallel to the optical axis in such a way that the third lens group is retracted out of the optical axis where the other lens groups (the first, second and third lens group) are positioned in a collapsed position. Moreover, the retractable frame is biased by a compression torsion spring provided on a main-guide shaft with a rotation biasing force to move it toward the optical axis where the other lens groups are positioned and a biasing force to move it along the main-guide shaft toward the collapsed position.
In photographing, an axial position of the lens group retained in the retractable frame is determined by a contact of the retractable frame biased by the rotation biasing force of the spring to a sub-guide shaft member with a guide function along the optical axis of the other lens groups. In collapsing, the retractable frame is rotated around the main-guide shaft against the rotation biasing force of the spring to be retracted out of a maximum diameter of the lens barrel. As a result, comparing with that a retracted position of the conventional retractable lens groups is within the maximum diameter of the lens barrel, it is possible to inhibit diameter-increasing of the lens barrel.